Prevent crashes during exit due to deregistering frames on exit (v2)

[marxin]

Second attempt suggested by @zebreus. Tested that locally and works reliably it seems.

Fixes: #5877

[Copilot]

Pull request overview

This PR prevents crashes during program exit by skipping unwind frame deregistration when exit() has been called. The fix uses an atexit handler to track when the program is exiting and early-returns from UnwindRegistry::Drop to avoid race conditions with internal unwinder state during shutdown.

Key changes:

• Adds an atexit handler to detect when program exit is initiated
• Skips frame deregistration in Drop when exit has been called
• Uses AtomicBool with SeqCst ordering to coordinate between the exit handler and Drop

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[zebreus]

I am pretty sure this is dead code, as we never make push anything into self.registrations when we are on macos aarch64

[zebreus]

@Syrus I think the correct fix would be to move the call to self.compact_unwind_mgr.deregister(); outside of the loop (potentially also add the registrations to self.registrations on macOS aarch64). However, I can't really test this as I don't have a Mac.

[marxin]

Fair point. I would like to handle this in a separate PR as it's pretty unrelated to it.
@zebreus Does it work for you?

[marxin]

Hm, it's causing a new segfault:

./run.sh: line 3: 15775 Segmentation fault      (core dumped) $WASMER -q run main.wasm --dir . -- failing_exec
Testing fork...
Testing fork ❌

@zebreus I was unable to reproduce it locally (running it 1000x). Can you check it?

[zebreus]

I reran the CI job on this PR and it seems consistently broken. Not sure why, it seems completly unrelated to the change

[zebreus]

Rebased this PR on the latest main, maybe that fixes it

[zebreus]

I pushed an extra commit that reverts all changes to check if that makes CI pass to be sure that the changes actually cause the crash